Use this card during your opponent's turn to send a Level 4 "Alien" to your Graveyard, then during your next turn banish this card to search "Alien Ammonite" to help you Synchro Summon a Level 5 monster like "Cosmic Fortress Gol'gar".
You could also send a Level 2 or higher "Alien" and search "Alien Overlord" that can be summoned removing the A-Counters.
If you already have Code A Ancient Ruins, you can send Alien Hypno to your Graveyard with this card, then on your next turn Special Summon Alien Hypno using 2 of the A-Counters you placed. Now you can Normal Summon Alien Hypno to get it's Gemini Effect, banish this card from your graveyard to add Alien Overlord to your hand and use the remaining 2 A-Counters to Special Summon it. With Alien Overlord's effect, you can put an A-Counter on all your opponent's face-up monsters and then use Alien Hypno to take control of all of them.
If your opponent doesn't have many monsters, you can instead banish this card to search for Alien Ammonite to bring out Cosmic Fortress Gol'gar then use Code A Ancient Ruins to Special Summon Alien Hypno, use Cosmic Fortress Gol'gar's effect to return Code A Ancient Ruins to your hand, then replay Code A Ancient Ruins to Special Summon Alien Ammonite so you can Synchro Summon a second Cosmic Fortress Gol'gar out. You can now return Code A Ancient Ruins to your hand again to either destroy 1 card with Gol'gar's effect or summon Alien Hypno from the Graveyard again.